This invention relates to patient monitoring systems, particularly to such systems that use automatic sensing devices to provide a signal indicating the movements or absence of a patient, or body conditions of the patient.
It is to interest to hospitals and other institutions that the movements of persons confined to a bed or to any constrained location or position be controlled and monitored to indicate the physical activities and body condition of these persons. At present, elaborate arrangements are necessary to monitor many conditions of patients and often a desired or necessary monitoring is not used because of cost or unavailability of necessary equipment. Some prior art devices have been developed that use magnets attached to persons being monitored, physical connections of various types, or mechanically actuated switching devices that respond to the presence or absence of a patient from his bed or chair.
All of the known prior art devices suffer from various deficiencies. The need to make physical connections is obviously burdensome and is usually defeated by the activity of the patient. Also, these systems require special equipment so as to limit their availability to many hospitals. One device uses a capacitor that is deformed by pressure so that its capacitance changes when the deforming force is removed. This change is sensed to indicate the absence of the patient. However, this device is of limited application and requires a source of constant electrical potential.